The present invention relates to a magnetic recording/reproducing method using a soft magnetic material in which magnetization direction is not used as a recording means. More particularly, the present invention relates to a magnetic recording/reproducing method, reproducing apparatus used therefor, a magnetic recording medium and a method for producing the same capable of recording an information signal by means of a pattern of soft magnetic material, and capable of easily making a large number of copies of the same information.
In the technical field of an optical disc or a magnetic recording apparatus, as a result of highly developed information-related techniques, a technique for mass recording data is increasingly important. Further, tracking servo techniques for positioning a recording head are indispensable for the purpose of recording data with high density.
An optical disc is an example of achieving the afore-mentioned needs with low cost. In the case of producing the optical disc, a master disc having concave parts and convex parts called a guiding groove, guiding pit or the like for necessary data or a servo is prepared by means of a laser direct drawing technique with high precision in the mastering process, followed by transfering the master disc to a plastic disc by means of injection molding, so that mass production can be achieved. The reason why the concave parts and the convex parts are reproduced in the optical disc with good condition, or servo operation can be performed by using the concave parts and the convex parts with good condition is marked change of intensity of the light beam reflected on the concave parts and the convex parts caused by diffraction
Further, as seen in a video tape recorder, floppy disc and the like, in a magentic recording apparatus, copies of mass recorded data can be made. However, in magnetic recording, magnetic patterns of information should be written one by one by using the magnetic head, said pattern being composed of fine magnetics. Therefore, it is impossible to make such a large amount of copies that are performed by the optical disc. For that reason, copies in magnetic recording tend to be expensive. In the tracking servo of magnetic head, the pattern, which should be precisely written by the magnetic head on the magnetic medium, is usually used. There arises such a problem that the patterns are moved from the predetermined position by vibration or the like when the servo patterns are written.
On the other hand, convex parts and concave parts using the magnetic head in the magnetic disc has been performed. For instance, as disclosed in "Digest of the Intermag conference, Paper #FD-10, Stockholm Sweden (April, 1993)" or "Japanese Association of Promoting Science, the 144th committee of magnetic recording, the document number 104 (Nov. 25, 1993)", an address mark or a pit for positioning is prepared by the same method as the optical disc, followed by reading the convex parts and concave parts by the magnetic head (referring to FIG. 16).
In this method, the following two means are employed for the purpose of reading a slight change of magnetic flux caused by the magnetization of the convex parts and a concave parts of the magnetic head 41 such as shown in FIG. 16.
One is optimizing the shape of a slider (not shown in FIG. 16) carrying the head portion so that spacing of about 0.1 .mu.m even on the convex parts and the concave parts can be stably obtained.
The other is recording by using the magnetic head so that the magnetization directions of a concave part and a convex part are anti-parallel with each other as shown in FIG. 17(b). In this specification anti-parallel means that the magnetization directions are opposed to each other in the same plane. For example, the magnetization directions of the concave parts and the convex parts are made to align in the same direction by applying an initial large magnetic field as shown in FIG. 17(a). This is followed by applying a small magnetic field so that only in the convex parts magnetization directions are reversed as shown in FIG. 17(b). By virtue of the magnetic head with spacing substantially the same as the difference between a height of the convex part and a height of the concave part, a large magnetic field can be applied to the convex part and small magnetic field can be applied to the concave part. Even in the magnetic head, a large signal can be obtained by making the magenetization directions of the convex parts and the concave parts anti-parallel to each other.
By using the above-mentioned method, there arises no such a problem that the patterns are moved from the predetermined position by the vibration in case of writing a servo pattern. For that reason, the servo operation can be performed in good condition. However, even in the method of using the convex parts and the concave parts, the magnetic patterns should be recorded by using a hard magnetic material in the surface, followed by applying a magnetic field.
Further, there is disclosed the other apparatus in Japanese Unexamined Patent Publication No. 77615/1974. As shown in FIG. 18, the apparatus comprises a permanent magnet 43, a Hall element 44, a magnetic member 45 made of a material having high permeability and a thin magnetic film 46 made of a material having high permeability. Since the apparatus is used for reproducing of magnetic card, a large pattern of several hundred micro meters to 1 mm is reproduced. For that reason, in the apparatus there is provided first and second gaps in a magnetic circuit. The Hall element is located in the first gap interposed between the permanent magnet 43 and the magnetic member 45. Between the permanent magnet 43 and the magnetic member 45, there is formed the second gap for detecting the thin magnetic film. The magnetic circuit is formed with interposing the gaps. When the thin magnetic film comes near the second gap between the permanent magnet and the magnetic member where the card is located, a large amount of the magnetic flux flows in the Hall element. While on the other hand, when the thin magnetic film is not located in the place near the second gap, there is a small flow of the magnetic flux flowing into the Hall element since a magnetic reluctance is large in the magnetic circuit. The large and small magnetic fluxes flowing into the Hall element are transformed to a large and small Hall voltage as an electric signal.
According to the conventional apparatus provided with the convex parts and the concave parts on the magnetic disc, it is required to keep the magnetic head floating with spacing of about 0.1 .mu.m. For that reason, it is required to make the recording medium and the magnetic head close for the purpose of avoiding an effect caused by fine particle such as dust, so that it is impossible to exchange the recording medium. Further, in order to make the magnetization directions of the convex parts and the convave parts anti-parallel to each other, it is required to employ the magnetic head for writing a magnetization. Therefore, there is a problem in which the many copies each having information identical with each other will be produced with increased cost. Further, there arises the problem that the magnetic patterns are erroneously cancelled by an effect of the external magnetic field since the magnetic patterns written on the magnetic medium are employed as information.
On the other hand, the conventional apparatus using a Hall element includes an insulating film formed on both sides of the Hall element and the first gap with spacing of at least 100 .mu.m to several hundred micro meters for the purpose of connecting with a lead or lead wire. For that reason, the magnetic reluctance in the magnetic circuit becomes large. When the spacing of the second gap located in the side of the card (recording medium) is small, changing of the Hall voltage depending on the presence of the thin magnetic film is small, and a desired SN ratio is difficult to obtain. Accordingly, the spacing of the gap on the card side is required to range between several hundred micro meters to about 1 mm, so that the information with high density cannot be reproduced.
The object of the present invention is to solve the above-mentioned problem, and to provide a magnetically recording/reproducing method in which a large number of copies can be easily made in the same manner as an optical disc, and so in which information with high density can be recorded and reproduced while using magnetism.
Another object of the present invention is to provide a magnetic reproducing apparatus used for the above-mentioned magnetically recording/reproducing method in which information with high density recorded in a magnetic recording medium can be surely reproduced from the magnetic recording medium.
Yet another object of the present invention is to provide a magnetic recording medium and method for the same in which a large amount of copies can be made and information can be recorded with high density.